Snotlout's dragon, Hookfang, is shedding scales-and that's causing fires in Berk! When an upset Hookfang flies off and disappears, the gang set up a search party. Unfortunately, Alvin the Treacherous is also on the hunt for Hookfang . . . Who will get to Hookfang first-the Riders or Alvin?
On Berk, Vikings do their everyday things, but Hiccup remarks that there's bound to be something out of the ordinary. Dragons soar above Berk, a sign that Berk is truly living in harmony with dragons. Vikings, he adds, have learnt to adapt.
Each of the dragon riders show off new tricks at sea while returning to Berk. Hiccup shows Toothless' new skill of sea-skimming (like skipping rocks). Astrid shows Stormfly's new skill of creating waterspouts. Fishlegs shows off Meatlug's new skill of firing heated rocks like bullets. Tuffnut and Ruffnut show off Barf and Belch's new skill of breathing fire directly.
When they finally get back to Berk, Hookfang, over the Hooligan village, starts shedding flaming scales everywhere. The scales light several houses and buildings on fire. Mildew tells the villagers that he told them that the dragons will bring doom and destruction upon them.
Stoick then has Gobber tell the dragon riders that until Hookfang's shedding halts, he is to be isolated from the other dragons. Snotlout protests this.
Hookfang then goes out to sleep in a cave at sea while the other dragons sleep cosily on Berk in their riders' houses.
In the morning Snotlout goes to visit Hookfang with a rat to feed to him, only to discover Hookfang has left. Hiccup tries to comfort Snotout. Snotlout replies that he is over Hookfang. Hiccup doesn't believe Snotlout on this and again tries to comfort Snoutlout, saying he will start a search party.
Hiccup and the rest of the academy search for Hookfang, but a storm forces them back to Berk.
Back on Berk, Stoick is angry with Hiccup and the rest of the dragon riders for flying during the worst storm they've seen since the "Great Deluge." Stoick then grounds all the riders.
Hiccup tells Snotlout that that they will have to wait out the storm before searching again. Snolout responds angrily, telling Hiccup it's his fault that Hookfang went missing, saying that if it were Toothless in that position, Hiccup would've found a way to keep Toothless on Berk. Astrid tries to comfort Hiccup, telling Hiccup that Snotlout is wrong, only to have Hiccup tell her that Snotlout is right.
Meanwhile, Alvin the Treacherous and the Outcasts are out at sea searching for Hookfang during the storm. Alvin's spies told him about what happened to Hookfang. Alvin tells his men, he intends to capture Hookfang to use as bait for Hiccup. The Outcasts then come across Hookfang, who they attack. Hookfang then sheds a bit, with Alvin ordering the Outcasts to catch as many of Hookfang's scales as they can. The Outcasts' attack sends Hookfang into the volcano of an island the attack pushed him to. Alvin then uses the scales to leave a trail for Hiccup to follow.
Hiccup, feeling like he "has to do something," defies his father's orders and goes out to search for Hookfang. Toothless picks up a scent that leads them to the trail of scales Alvin set. Hiccup and Toothless follow the trail to the island where Hookfang was situated in. Hiccup proceeded to enter the volcano to convince Hookfang to come out, telling Hookfang that it's dangerous for him to be in there. Beaten by the heat, Hiccup exits the volcano, only to be met by the Outcasts. Hiccup orders Toothless to sea-skim back to Berk, while he is captured by Alvin.
Toothless sea-skims back to Berk and the rest of the gang, who had already guessed that Hiccup left without them, spot him in the horizon. They quickly rescue the exhausted Toothless who passed out as he approached the island. Upon hearing the news, Stoick orders the fastest ships to prepare to set sail, while he plans to punish him. Gobber and the other Riders try to convince him otherwise.
Meanwhile, Alvin and the Outcasts prepare to leave the island, but his crew remarks that the weather is not in favour. Hiccup whose hands are tied up, is slowly burning them against a hot rock and taunts Alvin, that they are sitting at the foot of a volcano with a highly combustible dragon in it. The volcano erupts almost immediately and Alvin orders to set sail. Hiccup, in the nick of time, broke free and raced towards the mountain peak, only to be cornered by the Outcasts once again. The captors seize him and set sail. Alvin begins to announce his plan to use Hiccup to train dragons to defeat Berk, when the rest of the gang shows up.
They had been sent by Stoick, who was on the ship with Toothless. Using the special skills they had practiced that morning, they quickly obliterate the ships.
In the heat of the battle, Astrid swoops onto one of the ships and frees Hiccup. Without notice, Alvin turns up behind them, armed with a sword. Thankfully, Stormfly sends a quiver of spines towards him and Hiccup reunites with Toothless on the ship. Their reunion was short-lived, as the duo set off to aid with the battle. After destroying the ships, the Riders rush to retrieve Hookfang. Snotlout was about to head into the caves, when Hiccup stopped him, and he threatened the latter about him not doing the same to Toothless. Hiccup firmly asserts that they need a plan.
Soon, they gather up dragon scales, driftwood and tar and create a fireproof shield made out of Nightmare scales lined against the wood. Snotlout and Hiccup hide behind the shield and brave into the cave. The shield starts to melt, but the duo made it to Hookfang in time. Snotlout then expressed his heartfelt apologies on leaving him behind.
Outside the volcano, Stoick wants to charge in, despite the others' relentless pleas. The duo emerged from the cave, with Hookfang, much to the team relief. Snotlout then turns towards Hiccup and hisses not to say a anything about the sincere words he had spoken about in the cave.
Back on Berk, Hiccup closes his narration. He, along with Snotlout, patch up the burnt roofs of houses with Nightmare scales and remarking the Vikings learn to adapt.
- Hiccup Horrendous Haddock III
- Astrid Hofferson
- Snotlout Jorgenson
- Fishlegs Ingerman
- Tuffnut Thorston
- Ruffnut Thorston
- Stoick the Vast
- Gobber the Belch